Staphylococcus-Streptococcus- Enterococcus

Bacteriology I

Cocci

Gram positive cocci

Gram-positive cocci Aerobic: -catalase positive: Staphylococcus,Micrococcus -catalase negative: Streptococcus, Enterococcus Anaerobic: Anaerococcus,Peptostreptococcus

Catalases Enzymes: that catabolize hydrogen peroxide into water and oxygen gas. If a drop of a peroxide solution is placed on a catalase-producing bacterial colony: - bubbles will appear when the oxygen gas is formed. Catalase:important virulans factor:h2o2 microbicidal and its degradation limits the ability of neutrophils to kill.

Gram positive Grow pattern Nonmotile Staphylococcus Aerobic or facultatively anaerobic Catalase-positive Grow in 10 % NaCl medium cluster of grapes single cells, pairs, short chains

Staphylococcus Present on the skin and mucous membranes of humans Nose is the main site of colonization for S. aureus. 40 species

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Staphylococcus S.aureus: -coagulase positive :clot forms (When a colony of S. aureus is suspended in plasma, coagulase binds to a serum factor, and this complex converts fibrinogen to fibrin, resulting in the formation of a clot.) Coagulase negative staphylococci

Most common Staph. causing diseases S. aureus Produce coagulase S. epidermidis S. saprophyticus S. capitis S. haemolyticus Coagulase negative staphylococcus

Methicillin-resistant S. aureus (MRSA) Beta-lactamase resistant penicillins such as methicillin Contain meca gene is notorious for producing serious infections in hospitalized patients and more recently outside the hospital in previously healthy children and adults.

meca gene methicillin-resistant S. aureus (MRSA) strains previously restricted to hospital-acquired infections are now present in the community and are responsible for the majority of staphylococcal infections.

Staphylococcus/IDENTIFICATION Microscopy Culture: Nutritionally enriched agar media with sheep blood Selective media (e.g., mannitol-salt agar)(chapman agar) Aerobic and anaerobic Large, smooth colonies Identification Positive coagulase S. aureus

Disease Hospital- and community-acquired infections with MRSA are a significant worldwide problem

Epidemiology Normal flora on human skin and mucosal surfaces Organisms can survive on dry surfaces for long periods Person-to-person spread through direct contact or exposure to contaminated fomites (e.g., bed linens, clothing) Risk factors include presence of a foreign body (e.g., splinter, suture, prosthesis, and catheter), previous surgical procedure, and use of antibiotics that suppress the normal microbial flora

MRSA: Vancomycin, trimethoprim-sulfamethizole, clindamycin, linezolid, daptomycin, or quinupristin-dalfopristin The focus of infection (e.g., abscess) must be identified and drained Treatment is symptomatic for patients with food poisoning (although the source of infection should be identified so that appropriate preventive measures can be enacted) Proper cleansing of wounds and use of disinfectant help prevent infections Thorough handwashing and covering of exposed skin help medical personnel prevent infection or spread to other patients

Coagulase-Negative Staphylococci Biology, Virulence, and Disease Relatively avirulent, although production of a "slime" layer can allow adherence to foreign bodies (e.g., catheters, grafts, prosthetic valves and joints, shunts) and protection from phagocytosis and antibiotics Infections include subacute endocarditis, infections of foreign bodies, and urinary tract infections

Epidemiology Normal human flora on skin and mucosal surfaces Organisms can survive on dry surfaces for long periods Person-to-person spread through direct contact or exposure to contaminated fomites, although most infections are with the patient's own organisms Patients are at risk when a foreign body is present The organisms are ubiquitous, so there are no geographic or seasonal limitations

Staphylococcus aureus infections

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Streptococcus Gram positive Grow pattern pairs, chains Most species are facultatively anaerobes Some grow only in atmosphere enhanced with CO 2 (capnophilic growth) Nutritional requirements are complex Blood, serum Catalase-negative

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Streptococcus Classification is complicated 3 different schemes are used 1.Lancefield groupings according to serologic properties- C carbohydrate(serologic typing) (A-W) 2.Hemolytic patterns: b*, a** & g hemolysis 3.Biochemical properties b* :complete hemolysis-transparent A**: partial hemolysis-green

S. pyogenes (group A streptococci) Pharyngitis, scarlet fever, pyoderma, erysipelas, cellulitis, necrotizing fasciitis, streptococcal toxic shock syndrome, bacteremia, rheumatic fever, glomerulonephritis

Streptococcus pyogenes infections

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S. agalactiae (group B) Neonatal infections (meningitis, pneumoniae, bacteremia) Urinary tract infections Amnionitis, Endometritis Wound infections

S.pyogenes Most common cause of bacterial pharyngitis Life threatening disease caused by these flesheating bacteria

Streptococcus pyogenes: group A Streptococcus streptococcal pharyngitis Rapid antigen test:group antigen Culture (gold standart: the most sensitive and specific Two swabs

Enterococcus Most frequently isolated & most commonly responsible for human disease with streptococcus among gram-positive cocci enteric cocci Possess the group D cell wall antigen 16 species in the genus E. faecalis & E. faecium are most commonly isolated

Enterococcus/Pathogenesis&Immunity Are commensal with limited potential for causing disease Do not possess toxins Cannot avoid being engulfed & killed by phagocytic cells BUT, Cause Serious Disease

Enterococcus/Clinical Diseases Can cause life-threatening infections One of the most feared nosocomial pathogens 10% of all nos. infct. Most commonly involved sites Urinary tract Blood stream A sever complication: endocarditis( following bacteremia)

Enterococcus Epidemiology Colonizes the gastrointestinal tracts of humans and animals; spreads to other mucosal surfaces if broad spectrum antibiotics eliminate the normal bacterial population Patients at increased risk include those hospitalized for prolonged periods and treated with broadspectrum antibiotics (particularly cephalosporins, to which enterococci are naturally resistant)

Enterococcus Therapy for serious infections requires combination of an aminoglycoside with a cell-wall-active antibiotic (penicillin, ampicillin, or vancomycin); newer agents include linezolid, quinupristin/dalfopristin, and selected fluoroquinolones Antibiotic resistance to each of these drugs is becoming increasingly common, and infections with many isolates (particularly E. faecium) are not treatable with any antibiotics

Vancomycin resistant enterococci(vre) The resistance in E. faecium to aminoglycosides and vancomycin is particularly troublesome, because it is mediated by plasmids and can be transferred to other bacteria.

Prevention, and Control It is difficult to prevent and control enterococcal infections. Careful restriction of antibiotic therapy and the implementation of appropriate infection-control practices (e.g., isolation of infected patients, use of gowns and gloves by anyone in contact with patients) can reduce the risk of colonization with these bacteria, but the complete elimination of infections is unlikely.

Hospital Infection MRSA VRE Rapid detection by real-time PCR

Streptococcus pneumoniae Encapsulated, Gr + coccus in pairs or short chains a-hemolytic Can grow only on enriched media (with blood products) Catalase (-) Capsule, classified accr. to polysaccharides 90 serotypes Capsular polysaccharides are used in vaccines

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S. pneumoniae / diseases Pneumoniae Meningitis Sinusitis Otitis media Bacteremia

S. pneumoniae / diseases Children and the elderly are at greatest risk for meningitis People with hematologic disorder (e.g., malignancy, sickle cell disease) or functional asplenia are at risk for fulminant sepsis Although the organism is ubiquitous, disease is more common in cool months

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Streptococcus pneumoniae Penicillin is the drug of choice for susceptible strains, although resistance is increasingly common Immunization is recommended for all children younger than 2 years of age and for adults at risk for disease

Gram negative cocci

Neisseria species are aerobic, Gram-negative diplococci with adjacent sides flattened together (resembling coffee beans). The bacteria are not motile and do not form endospores.

Neisseria meningitidis Biology, Virulence, and Disease Gram-negative diplococci with fastidious growth requirements Grows best at 35 C to 37 C in a humid atmosphere Oxidase and catalase positive; acid produced from glucose and maltose oxidatively

Neisseria meningitidis Biology, Virulence, and Disease Capsule protects bacteria from antibody-mediated phagocytosis Specific receptors for meningococcal pili allow colonization of nasopharynx Bacteria can survive intracellular killing in the absence of humoral immunity Endotoxin mediates most clinical manifestations

Epidemiology Humans are the only natural hosts Person-to-person spread occurs via aerosolization of respiratory tract secretions Highest incidence of disease is in children younger than 5 years, institutionalized people, and patients with late complement deficiencies Meningitis and meningococcemia most commonly caused by serogroups B, C, and Y; pneumonia most commonly caused by serogroups Y and W135; serogroups A and W135 associated with disease in underdeveloped countries Disease occurs worldwide, most commonly in the dry, cold months of the year

Endemic meningococcal disease occurs worldwide, and epidemics are common in developing countries. N. meningitidis is transmitted by respiratory droplets among people in prolonged close contact, such as family members living in the same household and soldiers living together in military barracks.

Humans are the only natural carriers for N. meningitidis. Studies of the asymptomatic carriage of N. meningitidis have shown that there is a tremendous variation in its prevalence, from less than 1% to almost 40%.

Neisseria gonorrhoeae N. gonorrhoeae is a fastidious organism, requiring complex media for growth; it is adversely affected by exposure to dry conditions or fatty acids.

N. gonorrhoeae does not grow on blood agar but does grow on chocolate agar and other enriched supplemented media. The optimum growth temperature is 35 C to 37 C, with poor survival of the organism at cooler temperatures. A humid atmosphere supplemented with 5% carbon dioxide (CO2) is either required or enhances growth of N. gonorrhoeae. Although the fastidious nature of this organism makes recovery from clinical specimens difficult, it is nevertheless easy for the organism to be transmitted sexually from person to person.

Gonorrhea occurs naturally only in humans; it has no other known reservoir. It is second only to chlamydia as the most commonly reported sexually transmitted disease.

N. Gonorrhoeae. Nucleic acid amplification (NAA) assays specific for N. gonorrhoeae Combination NAA assays for both N. gonorrhoeae and Chlamydia organisms are available and have replaced culture in most labs. The primary problem with this approach is that it cannot be used to monitor antibiotic resistance of the identified pathogens.

N. gonorrhoeae Culture -genital specimens both non-selective media (e.g., chocolate blood agar) and selective media that suppress the growth of contaminating organisms (e.g., modified Thayer-Martin medium). A nonselective medium should be used because some gonococcal strains are inhibited by the vancomycin present in most selective media. The gonococci die rapidly if specimens are allowed to dry. Therefore drying and cold temperatures should be avoided by directly inoculating the specimen onto prewarmed media at the time of collection.